Cholecystokinin (CCK) is a neuropeptide which is widely distributed in the mammalian central nervous system. Two CCK receptors have been identified to mediate the effects of CCK/gastrin family: CCKA (or CCK-1) receptor and CCKB (or CCK-2 or gastrin receptor). The CCKA receptor has a more limited distribution with highest densities in the hypothalamic nuclei, areas of the hippocampus, the septum, dorsal motor vagal nucleus and interpeduncular nucleus of the brain stem. It also occurs in numerous gastro-intestinal tissues. CCKA receptors affect satiety, pancreatitis, gut motility and have growth-promoting effects on some tumors.